Hippopotamus
distribution
Before the last glaciation,
the hippo was wide-spread in North Africa and Europe,[2]
and it can live in colder climates on the condition that the water does not
freeze during winter. The species was common in Egypt's Nile region until
historic times but has since been extirpated. Pliny the Elder writes that, in
his time, the best location in Egypt for capturing this animal was in the Saite
nome (N.H. 28.121); and the animal could still be found along the Damietta
branch after the Arab Conquest (639). Even on the island of Malta, at Għar
Dalam (the Cave of Darkness), bone remains of hippopotamuses have been found,
dated to about 170,000 years old. Hippos are still found in the rivers and
lakes of Uganda, Sudan, Kenya, northern Democratic Republic of the Congo and Ethiopia,
west to Gambia as well as in Southern Africa (Botswana, Republic of South Africa,
Zimbabwe, Zambia). A separate population is in Tanzania and Mozambique.
A submerged
hippo. Adult hippos typically resurface to breathe every 3–5 minutes
Hippos leave the water at
dusk and travel inland, sometimes up to 8km, to graze on short grass, their
main source of food. They spend four to five hours grazing and can consume 68kg
of grass a night.[3]
Adult hippos are not
generally buoyant. When in deep water, they usually propel themselves by leaps,
pushing off from the bottom. They move at speeds upto 8 km/h in water. Young
hippos are buoyant and more often move by swimming, propelling themselves with
kicks of their back legs. One hippo calf survived after being pushed out to sea
during the tsunami generated by the 2004 Indian Ocean earthquake and was
rescued on a nearby island.[4]
Baby hippos are born
underwater at a weight between 25 and 45 kg (60−110 pounds) and must
swim to the surface in order to take their first breath. The young often rest
on their mothers' backs when in water that is too deep for them, and swim
underwater in order to suckle.
Adult hippos typically
resurface to breathe every 3–5 minutes. The young have to breathe every two to
three minutes. The process of surfacing and breathing is automatic, and even a
hippo sleeping underwater will rise and breathe without waking. Hippos have
been documented staying submerged for up to thirty minutes.[5]
A hippo closes its nostrils when it submerges.
Adult hippos are extremely
hostile toward crocodiles, which often live in the same pools and rivers as
hippopotami. This is especially so when hippo calves are around. Hippos also
seem to empathize with the prey of crocodiles and have been known to stand
guard over dead and dying antelope on river banks. Hippos have been known to be
very defensive towards humans, and according to the paper by Dr Ed Evans, hold
the title of African mammal which kills the most humans.[6]
To mark territory, hippos
spin their tails while defecating to distribute their excrement over the
greatest possible area.[7] Video of hippos excreting can
be found here and here.
A hippo's skull,
showing the large canine teeth used for fighting
Three species of hippos
(family Hippopotamidae) became extinct within the Holocene on Madagascar, one
of them as recently as about a thousand years ago. A dwarf species, Phanourios
minutis, existed on the island of Cyprus but became extinct at the end of
the Pleistocene. Whether this was caused by human intervention is debated (see Aetokremnos).
In 2005, the population of hippos in Democratic Republic of the Congo's Virunga
National Park had dropped to 800 or 900 individuals from around 29,000 in the
mid 1970s, raising concerns about the viability of that population. This
decline is attributed to the disruptions caused by the Second Congo War. The poachers
are believed to be former Hutu rebels, poorly paid Congolese soldiers and local
militia groups. Reasons for poaching include the belief that hippos are
unintelligent, that they are a harm to society, and also for money—a
three-tonne hippo is worth thousands of dollars.[citation needed]
The sale of hippo meat is illegal, but black-market sales are difficult for WWF
officers to track.
The
Hippopotamus Hunt
(1616), by Peter Paul Rubens
Five subspecies of hippos
have been described based on morphological differences (H. a. amphibius,
H. a. kiboko, H. a. capensis, H. a. tschadensis, H. a.
constrictus; Lydekker 1915). The existence of these putative subspecies has
been tested by genetic analyses. A recent paper by Okello et al. (2005)
describes the use of mitochondrial DNA from skin biopsies taken from 13
sampling locations, the authors consider genetic diversity and structure among
hippo populations across the continent. They find low but significant genetic
differentiation among 3 of the 5 putative groups - H. a. amphibius, H.
a. capensis, H. a. kiboko. If these findings are accurate, that
would mean that common hippos in Kenya and Somalia (kiboko), southern Africa
(capensis from Zambia to South Africa), and the rest of sub-Saharan African
countries (amphibius) represent three distinct subspecies, with H. a.
amphibus as the ancestral group. Okello et al. also find evidence that
common hippos in Africa experienced a marked population expansion during or
after the Pleistocene Epoch, which they attribute to an increase in water
bodies at the end of this era. These findings have important conservation
implications. Hippo populations across the continent are threatened by habitat
loss and unregulated hunting. In addition to addressing these common threats,
the genetic diversity of these three distinct subspecies will need to be
preserved. The hippopotamus has been moved on to the IUCN Red List drawn up by
the World Conservation Union (IUCN) in May 2006. This signifies that the common
hippopotamus is now in serious danger of extinction.